The forested Kaibab Plateau, north of the Grand Canyon. This plateau is a bit higher than the southern part, the Coconino Plateau, because the layers which were cut by the Grand Canyon are 1-2 degrees tilting to the south. This has another effect, namely that the Colorado river is closer to the southern rim than to the northern rim. So the geological structure explains why you have more dramatic slopes south of the Colorado in this part of the Canyon.
It is generally accepted that these plateaus were covered with younger layers which got ''peeled off'' by erosion is a phase called ''the Great Denudation''. You can still see those younger layers which got stripped away in the north, in the area of Bryce Canyon.